Fiber incorporating quantum dots as programmable dopants

ABSTRACT

A programmable dopant fiber includes a plurality of quantum structures formed on a fiber-shaped substrate, wherein the substrate includes one or more energy-carrying control paths ( 34 ), possibly surrounded by an insulator ( 35 ), which pass energy to quantum structures. Quantum structures may include quantum dot particles ( 37 ) on the surface of the fiber or electrodes ( 30 ) on top of barrier layers ( 31 ) and transport layer ( 32 ) which form quantum dot devices (QD). The energy passing through the control paths ( 34 ) drives charge carriers into the quantum dots (QD), leading to the formation of “artificial atoms” with real-time tunable properties. These artificial atoms then serve as programmable dopants, which alter the behavior of surrounding materials. The fiber can be used as a programmable dopant inside bulk materials, as a building block for new materials with unique properties, or as a substitute for quantum dots or quantum wires in certain applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of Provisional PatentApplication No. 60/312,264, filed Aug. 14, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for producing quantum effects, namelya fiber that is capable of carrying energy with an exterior surfacepopulated by quantum dot structures that are controlled by changes inthe energy carried by the fiber. The invention has particular, but notexclusive, application in materials science as a programmable dopantthat can be placed inside bulk materials and controlled by externalsignals.

2. Description of the Related Art

The fabrication of very small structures to exploit the quantummechanical behavior of charge carriers (e.g., electrons or electron“holes”) is well established. Quantum confinement of a carrier can beaccomplished by a structure whose linear dimension is less than thequantum mechanical wavelength of the carrier. Confinement in a singledimension produces a “quantum well,” and confinement in two dimensionsproduces a “quantum wire.”

A quantum dot (QD) is a structure capable of confining carriers in allthree dimensions. Quantum dots can be formed as particles, with adimension in all three directions of less than the de Broglie wavelengthof a charge carrier. Such particles may be composed of semiconductormaterials (including Si, GaAs, InGaAs, InAlAs, InAs, and othermaterials), or of metals, and may or may not possess an insulativecoating. Such particles are referred to in this document as “quantum dotparticles.” A quantum dot can also be formed inside a semiconductorsubstrate, through electrostatic confinement of the charge carriers.This is accomplished through the use of microelectronic devices ofvarious design, e.g., a nearly enclosed gate electrode formed on top ofa quantum well, similar to a P-N-P junction. Here, the term “micro”means “very small” and usually expresses a dimension less than the orderof microns, i.e., thousandths of a millimeter. The term “quantum dotdevice” refers to any apparatus capable of generating a quantum dot inthis manner. The generic term “quantum dot,” abbreviated QD in certaindrawings in this application, refers to any quantum dot particle orquantum dot device.

The electrical, optical, thermal, magnetic, mechanical, and chemicalproperties of a material depend on the structure and excitation level ofthe electron clouds surrounding its atoms and molecules. Doping is theprocess of embedding precise quantities of carefully selected impuritiesin a material in order to alter the electronic structure of thesurrounding atoms, for example, by donating or borrowing electrons fromthem, and therefore altering the electrical, optical, thermal, magnetic,mechanical, or chemical properties of the material. Doping levels as lowas one dopant atom per million atoms of substrate can produce measurablechanges in the expected behavior of the pure material, for example, byaltering the band gap of a semiconductor.

Quantum dots can have a greatly modified electronic structure from thecorresponding bulk material, and therefore different properties. Quantumdots can also serve as dopants inside other materials. Because of theirunique properties, quantum dots are used in a variety of electronic,optical, and electro-optical devices.

Kastner, “Artificial Atoms,” Physics Today (January 1993) points outthat the quantum dot can be thought of as an “artificial atom,” sincethe carriers confined in it behave similarly in many ways to electronsconfined by an atomic nucleus. The term “artificial atom” is now incommon use, and is often used interchangeably with “quantumdot.”However, for the purposes of this document, “artificial atom”refers specifically to the pattern of confined carriers (e.g., anelectron gas), and not to the particle or device in which the carriersare confined.

The term “programmable dopant fiber” refers to a wire or fiber withquantum dots attached to, embedded in, or formed upon its outer surface.This should not be confused with a quantum wire, which is a structurefor carrier confinement in two dimensions only.

Quantum dots are currently used as near-monochromatic fluorescent lightsources, laser light sources, light detectors (including infra-reddetectors), and highly miniaturized transistors, includingsingle-electron transistors. They can also serve as a useful laboratoryfor exploring the quantum mechanical behavior of confined carriers. Manyresearchers are exploring the use of quantum dots in artificialmaterials, and as programmable dopants to affect the optical andelectrical properties of semiconductor materials.

Kastner describes the future potential for “artificial molecules” and“artificial solids” composed of quantum dot particles. Specifics on thedesign and functioning of these molecules and solids are not provided.Leatherdale et. al., Photoconductivity in CdSe Quantum Dot Solids,”Physics Review B (15 Jul. 2000) describe, in detail, the fabrication of“two- and three-dimensional . . . artificial solids with potentiallytunable optical and electrical properties.” These solids are composed ofcolloidal semiconductor nanocrystals deposited on a semiconductorsubstrate. The result is an ordered, glassy film composed of quantum dotparticles, which can be optically stimulated by external light sources,or electrically stimulated by attached electrodes, to alter its opticaland electrical properties. However, these films are extremely fragile,and are “three dimensional” only in the sense that they have been madeup to several microns thick. In addition, the only parameter that can beadjusted electrically is the average number of electrons in the quantumdots. Slight variations in the size and composition of the quantum dotparticles mean that the number of electrons will vary slightly betweendots. However, on average the quantum dot particles will all behavesimilarly.

The embedding of metal and semiconductor nanoparticles inside bulkmaterials (e.g., lead particles in leaded crystal) is also wellestablished. These nanoparticles are quantum dots with characteristicsdetermined by their size and composition. They also serve as dopants forthe material in which they are embedded to alter selected optical orelectrical properties. However, there is no means or pathway by whichthese quantum dot particles can be stimulated electrically. Thus, thedoping characteristics of the quantum dots are fixed at the time ofmanufacture and cannot be adjusted thereafter.

In general, the prior art almost completely overlooks the broadermaterials-science implications of quantum dots. The ability to placeprogrammable dopants in a variety of materials implies a useful controlover the bulk properties of these materials. This control could takeplace not only at the time of fabrication of the material, but also inreal time, i.e., at the time of use, in response to changing needs andconditions. However, there is virtually no prior art discussing the use,placement, or control of programmable quantum dots in the interior ofbulk materials. Similarly, there is no prior art discussing theplacement of quantum dots on the surface of an electrically or opticallyconductive fiber.

U.S. Pat. No. 5,881,200 to Burt (1999) discloses an optical fiber (1)containing a central opening (2) filled with a colloidal solution (3) ofquantum dots (4) in a support medium. (See prior art FIGS. 1 and 2.) Thepurpose of the quantum dots is to produce light when opticallystimulated, for example, to produce optical amplification or laserradiation. The quantum dots take the place of erbium atoms, which canproduce optical amplifiers when used as dopants in an optical fiber.This fiber could be embedded inside bulk materials, but could not alterthe properties of such materials since the quantum-dot dopants areenclosed inside the fiber. In addition, no means is described forexciting the quantum dots electrically. Thus the characteristics of thequantum dots are not programmable, except in the sense that their sizeand composition can be selected at the time of manufacture.

U.S. Pat. No. 5,889,288 to Futatsugi (1999) discloses a semiconductorquantum dot device that uses electrostatic repulsion to confineelectrons. This device, as shown in prior art FIGS. 3 a and 3 b consistsof electrodes (16 a, 16 b, and 17) controlled by a field effecttransistor, both formed on the surface of a quantum well on asemi-insulating substrate (11). This arrangement permits the exactnumber of electrons trapped in the quantum dot (QD) to be controlled,simply by varying the voltage on the gate electrode (G). This is useful,in that it allows the “artificial atom” contained in the quantum dot totake on characteristics similar to any natural atom on the periodictable, and also to transuranic and asymmetric atoms which cannot easilybe created by other means. Unfortunately, the two-dimensional nature ofthe electrodes means that the artificial atom can exist only at or nearthe surface of the wafer, and cannot serve as a dopant to affect thewafer's interior properties.

Turton, “The Quanturn Dot,” Oxford University Press (1995) describes thepossibility of placing quantum dot devices in two-dimensional arrays ona semiconductor microchip, explicitly as a method for producing newmaterials through programmable doping of the substrate. This practicehas since become routine, although the spacing of the quantum dotdevices is typically large enough that the artificial atoms formed onthe chip do not interact significantly, nor produce macroscopicallysignificant doping. Such a chip also suffers from the limitation citedin the previous paragraph: its two-dimensional structure prevents itsbeing used as a dopant except near the surface of a material or materiallayer.

Goldhaber-Gordon et at., “Overview of Nanoelectronic Devices,”Proceedings of the IEEE, v. 85, n.4 (April 1997) describe what may bethe smallest possible single-electron transistor. This consists of a“wire” made of conductive C₆ (benzene) molecules, with a “resonanttunneling device” or RTD inline that consists of a benzene moleculesurrounded by CH₂ molecules that serve as insulators. The device isdescribed (incorrectly, we believe) as a quantum well rather than aquantum dot, and is intended as a switching device (transistor) ratherthan a confinement mechanism for charge carriers. However, in principlethe device should be capable of containing a small number of excesselectrons and thus form a primitive sort of artificial atom. Thus, theauthors remark on page 532 that the device may be “much more like aquantum dot than a solid state RTD.” The materials science implicationsof this are not discussed.

McCarthy, “Once Upon a Matter Crushed,” Science and Fiction Age (July1999), in a science fiction story, includes a fanciful description of“wellstone,” a form of “programmable matter” made from “a diffuselattice of crystalline silicon, superfine threads much finer than ahuman hair,” which use “a careful balancing of electrical charges” toconfine electrons in free space, adjacent to the threads. This isprobably physically impossible, as it would appear to violate Coulomb'sLaw, although we do not wish to be bound by this. Similar text by thesame author appears in McCarthy, The Collapsium,” Del Rey Books (August2000) and McCarthy, “Programmable Matter,” Nature (5 Oct. 2000).Detailed information about the composition, construction, or functioningof these devices is not given.

SUMMARY OF THE INVENTION

It is a general object of the present invention to use quantum dots toproduce a plurality of real-time programmable dopants in materials. Inone embodiment, an energy-transporting fiber is disclosed that controlsthe properties of quantum dot dopants using external energy sources,even when the dopants are embedded in solid materials, including opaqueor electrically insulating materials that would ordinarily isolate thequantum dots from external influences.

A programmable dopant fiber may be composed of a fiber-shaped materialwith a plurality of quantum dot particles or quantum dot devicespopulating the surface of the fiber. The fiber further contains one ormore control paths, which carry energy to the quantum dots in order tocontrol their confinement of charge carriers.

According to the present invention, charge carriers are driven intoquantum confinement in the quantum dots by the energy in the controlpaths such that they form artificial atoms that serve as dopants for thesurrounding materials. The atomic number of each artificial atom isadjusted through precise variations or modulations in the voltage acrossthe quantum dot that confines it. This alters the doping characteristicsof the artificial atoms.

In some embodiments of the present invention, the excitation level ofthe artificial atom is also controlled, either through additionalelectrical voltages or through optical or electromagnetic stimulation.Additionally, in some embodiments of the invention the energy in thecontrol paths creates electric fields which affect the quantumconfinement characteristics of the quantum dots, producing controlledand repeatable distortions in the size and shape of the artificialatoms, further altering their doping characteristics, with acorresponding effect on the surrounding materials. Since the electrical,optical, thermal, magnetic, mechanical, and chemical properties of amaterial depend on its electronic structure, and since the embedding ofdopants can affect this structure, the programmable dopant fiber offersa means of controlling the interior properties of bulk materials in realtime.

The present invention provides a three-dimensional structure for quantumdots that can be considerably more robust than a nanoparticle film. Forexample, a contiguous GaAs fiber or metal wire is held together byatomic bonds, as opposed to the much weaker Van der Waals forces whichhold nanoparticle films together.

The present invention also provides a method for the electrical and/oroptical stimulation of quantum dot particles embedded inside bulkmaterials. The fiber may consist of, or include, one or more wires,optical conduits, or other energy pathways that are electrically and/oroptically isolated from the material in which they are embedded. Thesepathways branch directly to the quantum dot particles or devices on thesurface of the fiber, providing the means to stimulate them.

The present invention further provides a method for embedding andcontrolling electrostatic quantum dot devices (and potentially othertypes of quantum dot devices) inside bulk materials, rather than attheir surfaces. With the present invention, the doping characteristicsof quantum dots inside a material can be controlled by external signals,and thus varied by a user at the time of use. Thus, the properties ofthe bulk material can be tuned in real time, in response to changingneeds or circumstances.

According to the present invention, the programmable dopant fiber can beused outside of bulk materials, in applications where quantum dots,quantum wires, and nanoparticle films are presently used. For example,the programmable dopant fiber can serve as a microscopic light source orlaser light source that is both long and flexible. Further, multipleprogrammable dopant fibers can be arranged on a surface to producetwo-dimensional materials analogous to nanoparticle films, but muchstronger.

Also, according to the present invention, multiple programmable dopantfibers can be woven, braided, or otherwise arranged intothree-dimensional structures whose properties can be adjusted throughexternal signals, forming a type of “programmable matter.” Thisprogrammable matter may be a bulk solid with electrical, optical,thermal, magnetic, mechanical, and chemical properties that can be tunedin real time through the adjustment of the energies in the controlpaths, which affect the properties of artificial atoms used as dopants.The resulting programmable materials, unlike nanoparticle films, cancontain artificial atoms of numerous and wildly different types, ifdesired. Thus, the number of potential uses for the programmable dopantfiber materials is vastly greater than for the materials based onnanoparticle films.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, closely related figures have the same element numbers,except for FIGS. 1-3B from the prior art.

FIGS. 1 and 2 are from the prior art, U.S. Pat. No. 5,881,200 to Burt(1999), and show a hollow optical fiber containing a colloidal solutionof quantum dots in a support medium.

FIGS. 3 a and 3 b are from the prior art, U.S. Pat. No. 5,889,288 toFutatsugi (1999), and show a semiconductor quantum dot device that useselectrostatic repulsion to confine electrons.

FIGS. 4 a and 4 b are schematic drawings of a first embodiment of thepresent invention detailing a multilayered microscopic fiber thatincludes a quantum well, surface electrodes, which form quantum dotdevices, and control wires to carry electrical signals to theelectrodes.

FIG. 4 c is a schematic drawing of an alternative to the embodiment ofFIGS. 4 a and 4 b including an optional memory layer.

FIGS. 5 a and 5 b are schematic drawings of a second embodiment of thepresent invention, in which quantum dot particles are positioned on thesurface of the fiber.

FIGS. 6 a and 6 b are schematic drawings of a third embodiment, in whichthe fiber comprises a single control wire with quantum dot particlesattached to its exterior surface.

FIGS. 7 a and 7 b are schematic drawings of still another alternativeembodiment of the present invention showing an ordered chain of quantumdot particles alternating with control wire segments.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 4 a (isometric view) and 4b (end view) show a preferred embodimentof the invention, which is a fiber containing control wires (34) in aninsulating medium (35), surrounded by a quantum well, plus an optionalmemory layer (33). The preferred composition of the insulator (35) is asemiconductor oxide, although a variety of other materials could beused. The preferred composition of the quantum well is a central ortransport layer (32) of a semiconductor (similar to the negative layerof a P-N-P junction), for example, GaAs, surrounded by barrier or supplylayers (31) of a semiconductor with higher conduction energy (similar tothe positive layers of a P-N-P junction). Because of the difference inconduction energies, electrons “fall” preferentially into the lowerenergy of the transport layer (32), where they are free to travelhorizontally (that is, within the layer) but are confined vertically(perpendicular to the layer) by the higher conduction energy of thebarrier layers. However, the present invention is not limited to thisparticular configuration, and includes quantum wells made from othermaterials and with other designs, as well as quantum wells designed totrap “holes” or other charge carriers.

The transport layer (32) of the quantum well must be smaller inthickness than the de Broglie wavelength of the charge carriers for thecharge carriers to be confined in it. For an electron at roomtemperature, this would be approximately 20 nanometers. Thicker quantumwells are possible, although they will only exhibit quantum confinementof the charge carriers at temperatures colder than room temperature.Thinner quantum wells will operate at room temperature, and at highertemperatures so long as the de Broglie wavelength of the carriers doesnot exceed the thickness of the transport layer (32).

The surface of the fiber includes conductors that serve as theelectrodes (30) of a quantum dot device. These electrodes (30) confinecharge carriers in the quantum well into a small space or quantum dot(QD) when a reverse-bias voltage is applied, since the negative chargeon the electrodes (30) repels electrons, preventing their horizontalescape through the transport layer. The electrodes (30) are powered bycontrol wire branches (36) reaching to the surface of the fiber from thecontrol wires (34) in the center of the fiber. In the preferredembodiment, the electrodes (30), control wires (34), and control wirebranches (36) are made of gold, although in principle they could be madeof other metals, or other materials, such as semiconductors orsuperconductors.

Once the charge carriers are trapped in a quantum dot (QD), they form anartificial atom that is capable of serving as a dopant. Increasing thevoltage on the electrodes (30) by a specific amount forces a specificnumber of additional carriers into the quantum dot (QD), altering theatomic number of the artificial atom trapped inside. Conversely,decreasing the voltage by a specific amount allows a specific number ofcarriers to escape to regions of the transport layer (32) outside thequantum dot (QD). One embodiment of the invention shown in FIG. 4 aprovides six electrodes (30) for each quantum dot device (QD), althoughmore or less could be used. By selecting the voltages applied to theseelectrodes (30) it is possible to alter the repulsive electric field,thus affecting size and shape of the quantum dot (QD) confinementregion. Changes to the confinement region similarly alter the size andshape of the artificial atom trapped inside the quantum dot (QD), eitherin conjunction with changes to the artificial atom's atomic number orwhile holding the atomic number constant. Thus, the doping properties ofthe artificial atom are adjusted in real time through variations in thesignal voltage of the control wires (34) at the fiber's center.

There are various possibilities for making the programmable dopant fiberof different materials, and in different configurations. The mostadvantageous configurations are the smallest, since smaller quantum dotscan contain charge carriers at higher energies (shorter de Brogliewavelengths) and thus display atom-like behavior at higher temperatures.The smallest conceivable programmable dopant fiber would be similar indesign to the single-electron transistor described in Goldhaber-Gordonet al., although molecules the size of benzene rings or smaller, ifemployed as quantum dot particles, will be unable to hold large numbersof excess charge carriers. This limits their usefulness in generatingartificial atoms. A somewhat larger but more practical design is toemploy electrically conductive nanotubes, such as a carbon nanotubes, asthe control wire segments (34), and fullerene-type molecules, such ascarbon fullerenes (for example, the quantum dot particles (37) of FIGS.5 a and 5 b).

FIG. 4 c shows the optional memory layer (33), which may be formed ofmicroscopic transistors or other switches placed inline with the controlwire branches (36) that are capable of turning voltages to the surfaceelectrodes (30) on and off. The ends of the control wire branch (36) mayserve as the source and drain electrodes of the switch, and anadditional control wire branch (36) is extended from a central controlwire (34) to serve as the gate electrode for the switch. The switch maybe a field effect transistor, although numerous other types of switchesmay be used without affecting the function of the invention. Thisswitching or memory layer is optional, since this switching can beaccomplished external to the fiber. However, it is included here forclarity. However, the present invention should not be limited to thisparticular configuration, and may include quantum dot devices made ofother materials or of alternative designs, including devices protectedby an additional insulating layer (not pictured), either continuous ordiscontinuous, on top of the electrodes (30) at the surface of thefiber.

Note that the exact arrangement of the various layers can be slightlydifferent than depicted here without altering the essential functioningof the programmable dopant fiber. For example, the cross-section may beany oval or polygon shape, and the insulated control wires (34) need notbe located at the fiber's center, although that may be the mostconvenient place to locate them.

The preferred manner of using the programmable dopant fiber is to placethe fiber or a plurality of fibers, as needed, inside a bulk material(e.g., a semiconductor), or to weave or braid them together into a two-or three-dimensional structure. Barrier layers (31) and transport layer(32) form a quantum well, which traps charge carriers in a quantum(wavelike) manner in the central or transport layer (32).

An electrical potential is then applied across the quantum wells throughthe control wires (34) from an external source. Energy motivated by theapplied voltage flows from the control wires (34) to the control wirebranches (36) and then to electrodes (30) on the surface of the fiber.Alternatively, the control wire branches (36) may pass through theoptional memory layer (33). The memory layer (33) may be composed ofin-line transistors or other switches, embedded in an insulating medium,which are capable of switching the electrical pathways open or closed.From the memory layer (33), the control wire branches (36) then lead tothe electrodes (30) at the surface of the fiber. Once the electricalpotential is applied across the electrodes (30), the change in voltagecreates an electrostatic repulsion that affects the carriers trapped inthe quantum well, herding them into small areas known as quantum dotswhere they form artificial atoms.

Adjustment of the voltages across the electrodes (30) can then affectthe characteristics of the artificial atoms, including: size; shape orsymmetry, number of charge carriers; and energy levels of the carriers.The resulting changes in the artificial atom can dramatically affect itsproperties as a dopant.

Depending on the number of control wires (34) inside the fiber and thenumber of quantum dot devices (QD) along its surface, the artificialatoms created in the confinement layer (32) may all be identical, mayrepresent multiple “artificial elements” in regular or irregularsequences, or may all be different. For example, if the signals sent toeach quantum dot device (QD) were identical, the artificial atoms on thefiber might all have an atomic number of 2, equivalent to helium, whichwould otherwise be extremely difficult to introduce as a dopant.Conversely, if two separate sets of control signals were sent, theartificial atoms could be an alternating pattern of helium (atomicnumber 2) and carbon (atomic number 6).

FIGS. 5 a (isometric view) and 5 b (end view) show an additionalembodiment of the invention, in which the fiber comprises multiplecontrol wires (34) surrounded by insulation (35), with control wirebranches (36) leading to quantum dot particles (37) on the surface ofthe fiber. An optional memory layer (not shown) may be included in thefiber of this embodiment as well. In this embodiment, the control wiresare conductors, but they could also be semiconductors, orsuperconductors, optical fibers, or other types of conduits for carryingenergy to stimulate the quantum dot particles (37). The dimensions cancover a broad range of microscopic values while retaining usefuloptical, electrical, and other properties for the programmable dopantfiber.

Because they are easily self-assembled in chemical solutions, thequantum dot particles (37) may be spherical nanocrystals consisting of acore of semiconductor material surrounded by a passivating shell ofcrystalline organic material. Dimensions of the core should not exceedthe de Broglie wavelength of the carriers to be confined within it.However, the invention is not limited to this particular configuration,and may include quantum dot particles of other shapes or made usingother materials and methods. Quantum dot particles may be deposited ontothe fiber, for example, by evaporation. Attachment to the fiber isreadily accomplished by means of van der Waals forces, although active“molecular tethers” may be added to the shell and/or fiber in order tobond the quantum dot particle (37) chemically to the insulator (35) orto the control wire branches (36).

The operation of this embodiment is very similar to the embodiment ofFIGS. 4 a-4 c, with the exception that the carriers are confined inquantum dot particles (37) rather than by electrostatic repulsion and aquantum well. Electrical (or optical) energy is applied to the controlwires (34) from an external source, and further to the surface of thefiber via control wire branches (36). An electrical potential is thencreated across the quantum dot particles (37). Placing the fiberadjacent to a grounded conductive or semiconductive material, includinganother programmable dopant fiber, produces a ground path from thecontrol wire branches (36) and then through the quantum dot particles(37). This creates the electrical potential across the quantum dotparticles (37) and forces the charge carriers into quantum confinementinside them, where they form artificial atoms. Increasing the voltageacross the control wires (34) drives additional carriers into thequantum dot particles (37), increasing the atomic number of theartificial atoms inside them.

Additionally, electrical or optical energy passed through the controlwires (34) can increase the excitation level of the artificial atoms.This stimulation can thus affect the properties of the artificial atomscontained in the quantum dot particles (37), including the number ofcarriers and the energy levels of the carriers. As before, the resultingchanges in the artificial atom can dramatically affect its properties asa dopant.

Depending on the number of control wires inside the fiber and the numberof quantum dot particles along its surface, the artificial atoms locatedin the quantum dot particles may all be identical, may representmultiple “artificial elements” in regular or irregular sequences, or mayall be different. In the case of the specific embodiment shown in FIGS.5 a and 5 b, there are four control paths. Therefore, each quarter-arcof the surface of the fiber may receive different control signals anddisplay different doping characteristics. Thus, the fiber may have up tofour “stripes” of different dopant running along its length.

FIGS. 6 a (isometric view) and 6 b (end view) show another additionalembodiment, in which quantum dot particles (37) are attached to thesurface of a non-insulated control wire (34). In general, this wire maybe an electrical conductor, but could be another type of conduit forcarrying energy to stimulate the quantum dot particles, for example, asemiconductor, superconductor, or optical fiber. Dimensions can onceagain cover a broad range of microscopic values.

Because they are easily self-assembled in chemical solutions, thequantum dot particles (37) may be spherical nanocrystals consisting of acore of semiconductor material surrounded by a passivating shell ofcrystalline organic material. Dimensions of the core should not exceedthe de Broglie wavelength of the carriers to be confined within it.However, the invention is not limited to this particular configuration,and may include quantum dot particles (37) of other shapes or made usingother materials and methods. Quantum dot particles (37) may be depositedonto the fiber, for example, by evaporation. Attachment to the fiber isreadily accomplished by means of van der Waals forces, although active“molecular tethers” may be added to the shell and/or fiber in order tobond the quantum dot particle (37) chemically to the control wire (34).

The operation of this embodiment is similar to that of FIGS. 5 a and 5b, with the exception that the fiber comprises a single control wire(34), with quantum dot particles (37) attached to its outer surface.Once again, the quantum dot particles (37) are stimulated by a current(or optical energy) passing through the control wire (34) to a groundpath that includes the quantum dot particles (37). This creates avoltage across the quantum dot particles (37) and forces the chargecarriers into quantum confinement inside them, where they formartificial atoms. Increasing the voltage across the control wire (34)drives additional carriers into the quantum dot particles (37),increasing the atomic number of the artificial atoms inside them.

This stimulation can then affect the properties of the artificial atomscontained in the quantum dot particles, including the number of carriersand the energy levels of the carriers. As before, the resulting changesin the artificial atom can dramatically affect its properties as adopant. The capabilities of this embodiment are more limited, in that(barring minor variations in the size and composition of the quantum dotparticles (37)) all the artificial atoms along the fiber cannot becontrolled separately or in subgroups, and will therefore have the samecharacteristics. No controlled patterning of different artificial dopantspecies is possible, except at the time of manufacture.

FIGS. 7 a (isometric view) and 7 b (end view) show still anotheradditional embodiment, in which control wire segments (38) alternatewith quantum dot particles (37). The dimensions of both the control wiresegments (38) and the quantum dot particles (37), while generallymicroscopic, could cover a broad range of values while retaining usefuloptical, electrical, and other properties for the programmable dopantfiber.

The operation of this embodiment is similar to that of FIGS. 6 a and 6b, with the exception that the quantum dot particles (37) are notattached to the surface of the fiber, but are an integral part of itsstructure, alternating with control wire segments (38). Because they areeasily self-assembled in chemical solutions, the quantum dot particles(37) may be spherical nanocrystals consisting of a core of semiconductormaterial surrounded by a passivating shell of crystalline organicmaterial. Dimensions of the core should not exceed the de Brogliewavelength of the carriers to be confined within it. Control wiresegments (38) may be metallic and bonded chemically to “moleculartethers” on the quantum dot particles (37). However, the invention isnot limited to this particular configuration, and may include quantumdot particles (37) and control wire segments (38) made and joined usingother materials and methods, including the molecular wires and quantumdots described by Goldhaber-Gordon et. al.

Electrical (or optical) energy may be applied to the control wiresegments (38) and directly to the quantum dot particles (37),stimulating them as described above. This stimulation can then affectthe properties of the artificial atoms contained in the quantum dotparticles (37), including the number of carriers and the energy levelsof the carriers. As before, the resulting changes in the artificial atomcan dramatically affect its properties as a dopant.

The capabilities of this embodiment are even more limited than theprevious one, in that resistive losses across each quantum dot particle(37) will cause the voltage to drop significantly across each segment ofthe fiber. Thus, each successive artificial atom along the length of thefiber will have a lower voltage (or, for example, illumination) than theone before it. Thus, the artificial atoms cannot be individuallycontrolled and will not be identical. Instead, the user may select asequence of artificial elements, of successively lower energies, to bepresented by the fiber. For example, the fiber might contain a number ofartificial atoms bearing atomic number 6, followed by a number bearingatomic number 5, and so on. This is far from the ideal form of aprogrammable dopant fiber, but it does provide a unique dopingcapability.

From the description above, the programmable dopant fiber can be seen toprovide a number of capabilities that are not possible with the priorart. First, the present invention provides the ability to placeprogrammable dopants in the interior of bulk materials and to controlthe properties of these dopants in real time, through external signals.In contrast, the properties of dopants based solely on quantum dotparticles can only be controlled at the time of manufacture.

Second, the present invention provides the ability to form programmablematerials containing “artificial atoms” of diverse types. In contrast,programmable materials based on nanoparticle films can contain onlymultiple instances of one “artificial element” at a time.

Also from the above description, several advantages over the prior artbecome evident. First, materials based on programmable dopant fiberswill, in general, be much stronger than materials based on nanoparticlefilms. Second, programmable dopant fibers can be used in numerousapplications where quantum dots and quantum wires are presentlyemployed. However, the programmable dopant fiber provides isolatedenergy channels for the optical or electrical stimulation of the quantumdots, permitting the quantum dots to be excited without also affectingthe surrounding medium or materials. For example, light can be passedthrough a quantum dot by means of the fiber, without also being shinedon or through surrounding areas, except through the fiber itselfSimilarly, an electrical voltage can be placed across a quantum dotwithout passing through the surrounding medium, except through thefiber. Thus, programmable dopant fibers can be used in numerousapplications where ordinary quantum dot devices or particles would notoperate, or would disrupt the surrounding material in uncontrolled ways.

Accordingly, it should be recognized that the programmable dopant fiberof this invention can be used as a real-time programmable dopant insidebulk materials, as a building block for new materials with uniqueproperties, and as a substitute for quantum dots and quantum wires invarious applications (e.g., as a light source or laser light source).

Although the description above contains much specificity, this shouldnot be construed as limiting the scope of the invention but merely asproviding illustrations of some of the presently preferred embodimentsof this invention. Numerous other variations may exist which do notaffect the core principles of the invention's operation. For example,the fiber could have non-circular shapes in cross-section, including aflat ribbon with quantum dots on one or both sides; the “artificialatoms” could be composed of charge carriers other than electrons; thecontrol wires could be replaced with semiconductor, superconductor,optical fiber, or other conduits for carrying energy; the control wirescould be antennas for receiving signals and energy from electromagneticwaves; any of the embodiments listed here could be replicated on amolecular scale through the use of specialized molecules such as carbonnanotube wires and fullerene quantum dot particles; the quantum dotscould be other sorts of particles or devices than those discussedherein, so long as they accomplish the quantum confinement necessary forthe formation of artificial atoms; and the number and relative sizes ofthe quantum dots with respect to the fiber could be significantlydifferent than in shown in the drawings.

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

1. A device for producing quantum effects, comprising: a materialfashioned into an elongated fiber shape; one or more control paths whichcarry energy along said material; a plurality of quantum dots,physically connected with said material and energetically connected tosaid control paths; wherein the energy carried in said control pathsactuate the quantum dots to trap and hold a controlled configuration ofcharge carriers, thus forming artificial atoms whose size, shape, atomicnumber, and/or energy level are dependent on the energies in saidcontrol paths.
 2. The device of claim 1, wherein said control paths areelectrical wires, whether conductors, semiconductors, orsuperconductors, which create electrical potentials across the quantumdots.
 3. The device of claim 2, wherein said electrical wires areconductive metallic wires.
 4. The device of claim 1, wherein saidcontrol paths are optical fibers carrying light or laser energy.
 5. Thedevice of claim 1, wherein said control paths are radio frequency ormicrowave antennas.
 6. The device of claim 1, wherein the quantum dotsare quantum dot particles.
 7. The device of claim 1, wherein the quantumdots are quantum dot devices.
 8. The device of claim 1, wherein only theatomic number and energy level of the artificial atoms can becontrolled.
 9. The device of claim 1, wherein only the energy level ofthe artificial atoms can be controlled.
 10. The device of claim 1,wherein the material further comprises: a first barrier layer; a secondbarrier layer; a transport layer located between the first barrier layerand the second barrier layer; and a plurality of electrodes connectedwith the control paths; wherein when energized, the plurality ofelectrodes interact with the first barrier layer, the second barrierlayer, and the transport layer to create at least one quantum well thatfunctions as a quantum dot device.
 11. The device of claim 1, whereinthe material further comprises a memory layer that switches the energycarried to a first confinement region from a first one to a second oneof the one or more control paths.
 12. The device of claim 1, whereinsaid one or more control paths comprises a single wire.
 13. The deviceof claim 1 further comprising an insulating medium, wherein said one ormore control paths are positioned in said insulating medium andinsulated from each other.
 14. The device of claim 1, wherein saidmaterial is embedded inside a bulk material, serving as a programmabledopant capable of altering the electrical, optical, thermal, magnetic,mechanical, and/or chemical properties of said bulk material in realtime based on the energies in said control paths.
 15. The device ofclaim 1, wherein said device comprises a plurality of fibers of saidsolid material woven, braided, stacked or arranged into two- orthree-dimensional structures.
 16. The device of claim 1, wherein saidfiber shape is of a shape selected from the group consisting of: a wire,a ribbon, and an optical fiber.
 17. The device of claim 1, wherein saidcontrol paths are carbon nanotubes.
 18. A device for producing quantumeffects, the device comprising: a material fashioned into an elongatedfiber shape; a plurality of quantum dots, physically connected with saidmaterial; at least one control path physically connected with saidmaterial and operatively coupled with said plurality of quantum dots,wherein said at least one control path is adapted to carry energy froman energy source to said plurality of quantum dots; and a plurality ofcharge carriers capable of being confined within said plurality ofquantum dots to form a respective plurality of artificial atoms; whereinsaid energy is adapted to stimulate each quantum dot of said pluralityof quantum dots to thereby confine a respective subset of said pluralityof charge carriers within each said quantum dot to form a respective oneof said plurality of artificial atoms; wherein said energy determinesthe size, shape, atomic number, and/or energy level of each artificialatom of said respective plurality of artificial atoms confined in eachrespective quantum dot; and wherein said plurality of artificial atomsalter the electrical, optical, thermal, magnetic, mechanical, and/orchemical properties of said material.
 19. The device of claim 18,wherein said at least one control path comprises a plurality of controlpaths; and each of said plurality of control paths is coupled to arespective one of said plurality of quantum dots.
 20. The device ofclaim 19 further comprising an energy source with a controllable,differentiable energy output coupled with each of said plurality ofcontrol paths, wherein said energy is differentiable between each ofsaid plurality of control paths and each said subset of said pluralityof charge carriers is differentiable between each respective quantumdot.
 21. The device of claim 18, wherein said at least one control pathcomprises a plurality of control paths; and each of said plurality ofcontrol paths is coupled to a respective group of said plurality ofquantum dots.
 22. The device of claim 21 further comprising an energysource with a controllable, differentiable energy output coupled witheach of said plurality of control paths, wherein said energy isdifferentiable between each of said plurality of control paths and eachsaid subset of said plurality of charge carriers is differentiablebetween each respective group of quantum dots.
 23. The device of claim18, wherein said at least one control path comprises a plurality ofcontrol paths; and a subset of said plurality of control paths iscoupled to a respective one of said plurality of quantum dots.